Generally speaking, in a semiconductor processing facility, a horizontal articulated link-type conveying robot is used for conveying a semiconductor wafer, a glass substrate for use in a display panel, or the like. In some cases, the distal end of a hand of the conveying robot is provided with a mapping sensor. The presence or absence of a substrate stored in a cassette is detected by the mapping sensor. For example, the hand includes two branching first and second distal end portions, and the mapping sensor is configured such that a sensor beam travels straight through space between the first and second distal end portions of the hand. In general, in the detection of an object by the mapping sensor, a position where the object blocks the sensor beam is recognized as a detected position of the object. Therefore, the position of the object in the direction of the beam of the mapping sensor cannot be specified. As one conventional technique, U.S. Pat. No. 752,267 discloses a technique of calculating the position of an object in an XY plane based on positions detected by a mapping sensor in two different orientations relative to the object (see Patent Literature 1, for example).